a. Field of the Invention
The instant disclosure relates to localization systems, such as those used in cardiac diagnostic and therapeutic procedures. In particular, the instant disclosure relates to systems, apparatuses and methods for detecting when a localization element(s), such as an electrode(s), emerges from and/or is retracted into an introducer sheath or other enveloping instrument.
b. Background Art
Catheters are used for an ever-growing number of procedures. For example, catheters are used for diagnostic, therapeutic, and ablative procedures, to name just a few examples. Typically, the catheter is manipulated through the patient's vasculature and to the intended site, for example, a site within the patient's heart. In many instances, the catheters are inserted into the body and navigated to the target location with the aid of an introducer sheath (sometimes referred to as simply an “introducer” or a “sheath”). As the ordinarily skilled artisan will appreciate, an introducer is a catheter with a central lumen through which other medical devices can be passed.
It is also known to track the three-dimensional coordinates of a catheter or other medical device moving within a patient's body using a localization system (sometimes also referred to as a “mapping system,” “navigation system,” or “positional feedback system”). These devices typically use magnetic, electrical, ultrasound, and other radiation sources to determine the coordinates of these devices. For example, impedance-based localization systems determine the coordinates of the medical device by interpreting a voltage measured by the medical device (more particularly, the voltages measured by one or more electrodes carried on the medical device) as a location within an electrical field.
One drawback of an impedance-based system, however, is that the impedance measurements become unreliable when the medical device is withdrawn into the introducer. This is because the introducer is normally made of an insulating material, such that the voltage gradient in the vicinity of localization electrodes within the sheath becomes non-linear and erratic. Indeed, a localization electrode within a sheath may appear to wander widely, making it difficult for the localization system to accurately and precisely render an image of the medical device for the practitioner. Although visual recognition of this condition is possible, there is no extant system or method to do so analytically.